By multimedia service delivery there is meant the delivery of multimedia contents including one or more of audio and/or images and/or video and/or text An example of multimedia contents delivery is the Multimedia Messaging Service (MMS) implemented in mobile telephony networks.
In the field of multimedia service delivery, it is known to perform a conversion (“transcoding”) of the multimedia contents from an original format to a transcoded format more suitable to the characteristics of, e.g., the user's communications terminal, and/or the communications link, and/or of the service class, and/or user's preferences.
The implementation of multimedia contents transcoding is motivated by several reasons, depending for example on the service and network context. For example, considering wireless multimedia delivery services, the transcoding can be made necessary by the variety of existing mobile communications terminals, thus by the differences in performance (different processing power, different I/O devices, and the like), and in the limited radio resources available. Thus, it is desirable that the information reaching the mobile communications terminal is already adapted to the terminal's characteristics, so as to reduce as much as possible the communications' bandwidth and the terminal's processing power.
The multimedia contents transcoding is based on transcoding policies that may in principle be objective policies (e.g. policies which can be described with a closed form mathematical equation), derived for example from the rate-distortion theory of C. E. Shannon, as described for example in R. Mohan et al., “Adapting Multimedia Internet Content for Universal Access”, IEEE Trans. On Multimedia, March 1999, pp. 104-114.
However, deriving a mathematical solution to the problem following such an approach is a rather complex task, so more heuristic approaches have been proposed.
For example, in U.S. Pat. No. 6,563,517 a method for dynamically adjusting transcoding parameters is described, wherein a policy module queries an image size predictor to estimate the size of an output image, and queries a network bandwidth analyzer to estimate the image transmission time to the client. Based on the estimates, the transcoding proxy decides whether or not to transcode the image.
In WO 02/056563 an information adaptation service selects multimedia objects stored in a multimedia database, and a transcoder/scalability service converts, recodes and/or scales the multimedia objects retrieved. The information adaptation service and the transcoder scalability service rely on a set of user preferences and a set of terminal and/or network capabilities (e.g., available bandwidth, bit error rate, display size, resolution, processing power, storage capacity).
US 2003/0227977 concerns a method for selecting a transcoding method from a set of transcoding methods. Weight factors, dependent of the data to be transcoded, are attributed to the transcoding methods; a mean value of at least one characteristic representative of each transcoding method is weighted by applying the weigh factors. The transcoding method is selected as a function of the weighted mean values.